enum.c

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/*
 * Asterisk -- An open source telephony toolkit.
 *
 * Copyright (C) 1999 - 2006, Digium, Inc.
 *
 * Mark Spencer <markster@digium.com>
 *
 * Funding provided by nic.at
 *
 * See http://www.asterisk.org for more information about
 * the Asterisk project. Please do not directly contact
 * any of the maintainers of this project for assistance;
 * the project provides a web site, mailing lists and IRC
 * channels for your use.
 *
 * This program is free software, distributed under the terms of
 * the GNU General Public License Version 2. See the LICENSE file
 * at the top of the source tree.
 */
 
/*! \file
 *
 * \brief ENUM Support for Asterisk
 *
 * \author Mark Spencer <markster@digium.com>
 *
 * \arg Funding provided by nic.at
 *
 * \par Enum standards
 *
 * - NAPTR records: http://ietf.nri.reston.va.us/rfc/rfc2915.txt
 * - DNS SRV records: http://www.ietf.org/rfc/rfc2782.txt
 * - ENUM http://www.ietf.org/rfc/rfc3761.txt
 * - ENUM for H.323: http://www.ietf.org/rfc/rfc3762.txt
 * - ENUM SIP: http://www.ietf.org/rfc/rfc3764.txt
 * - IANA ENUM Services: http://www.iana.org/assignments/enum-services
 *
 * - I-ENUM:
 *   http://tools.ietf.org/wg/enum/draft-ietf-enum-combined/
 *   http://tools.ietf.org/wg/enum/draft-ietf-enum-branch-location-record/
 *
 * \par Possible improvement
 * \todo Implement a caching mechanism for multile enum lookups
 * - See https://issues.asterisk.org/view.php?id=6739
 * \todo The service type selection needs to be redone.
 */
 
/*! \li \ref enum.c uses the configuration file \ref enum.conf
 * \addtogroup configuration_file Configuration Files
 */
 
/*!
 * \page enum.conf enum.conf
 * \verbinclude enum.conf.sample
 */
 
/*** MODULEINFO
    <support_level>core</support_level>
 ***/
 
#include "asterisk.h"
 
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/nameser.h>
#ifdef __APPLE__
#include <arpa/nameser_compat.h>
#endif
#include <resolv.h>
#include <ctype.h>
#include <regex.h>
 
#include "asterisk/module.h"
#include "asterisk/enum.h"
#include "asterisk/dns.h"
#include "asterisk/channel.h"
#include "asterisk/config.h"
#include "asterisk/utils.h"
#include "asterisk/manager.h"
 
#ifdef __APPLE__
#undef T_NAPTR
#define T_NAPTR 35
#endif
 
#ifdef __APPLE__
#undef T_TXT
#define T_TXT 16
#endif
 
static char ienum_branchlabel[32] = "i";
/* how to do infrastructure enum branch location resolution? */
#define ENUMLOOKUP_BLR_CC       0
#define ENUMLOOKUP_BLR_TXT      1
#define ENUMLOOKUP_BLR_EBL      2
static int ebl_alg = ENUMLOOKUP_BLR_CC;
 
/* EBL record provisional type code */
#define T_EBL      65300
 
AST_MUTEX_DEFINE_STATIC(enumlock);
 
/*! \brief Determine the length of a country code when given an E.164 string */
/*
 * Input: E.164 number w/o leading +
 *
 * Output: number of digits in the country code
 *     0 on invalid number
 *
 * Algorithm:
 *   3 digits is the default length of a country code.
 *   country codes 1 and 7 are a single digit.
 *   the following country codes are two digits: 20, 27, 30-34, 36, 39,
 *     40, 41, 43-49, 51-58, 60-66, 81, 82, 84, 86, 90-95, 98.
 */
static int cclen(const char *number)
{
    int cc;
    char digits[3] = "";
 
    if (!number || (strlen(number) < 3)) {
        return 0;
    }
 
    strncpy(digits, number, 2);
 
    if (!sscanf(digits, "%30d", &cc)) {
        return 0;
    }
 
    if (cc / 10 == 1 || cc / 10 == 7)
        return 1;
 
    if (cc == 20 || cc == 27 || (cc >= 30 && cc <= 34) || cc == 36 ||
        cc == 39 || cc == 40 || cc == 41 || (cc >= 40 && cc <= 41) ||
        (cc >= 43 && cc <= 49) || (cc >= 51 && cc <= 58) ||
        (cc >= 60 && cc <= 66) || cc == 81 || cc == 82 || cc == 84 ||
        cc == 86 || (cc >= 90 && cc <= 95) || cc == 98) {
        return 2;
    }
 
    return 3;
}
 
struct txt_context {
    char txt[1024];     /* TXT record in TXT lookup */
    int txtlen;     /* Length */
};
 
/*! \brief Callback for TXT record lookup, /ol version */
static int txt_callback(void *context, unsigned char *answer, int len, unsigned char *fullanswer)
{
    struct txt_context *c = context;
    unsigned int i;
 
    c->txt[0] = 0;  /* default to empty */
    c->txtlen = 0;
 
    if (answer == NULL) {
        return 0;
    }
 
    /* RFC1035:
     *
     * <character-string> is a single length octet followed by that number of characters.
     * TXT-DATA        One or more <character-string>s.
     *
     * We only take the first string here.
     */
 
    i = *answer++;
    len -= 1;
 
    if (i > len) {  /* illegal packet */
        ast_log(LOG_WARNING, "txt_callback: malformed TXT record.\n");
        return 0;
    }
 
    if (i >= sizeof(c->txt)) {  /* too long? */
        ast_log(LOG_WARNING, "txt_callback: TXT record too long.\n");
        i = sizeof(c->txt) - 1;
    }
 
    ast_copy_string(c->txt, (char *)answer, i + 1);  /* this handles the \0 termination */
    c->txtlen = i;
 
    return 1;
}
 
/*! \brief Determine the branch location record as stored in a TXT record */
/*
 * Input: CC code
 *
 * Output: number of digits in the number before the i-enum branch
 *
 * Algorithm:  Build <ienum_branchlabel>.c.c.<suffix> and look for a TXT lookup.
 *      Return atoi(TXT-record).
 *      Return -1 on not found.
 *
 */
static int blr_txt(const char *cc, const char *suffix)
{
    struct txt_context context;
    char domain[128] = "";
    char *p1, *p2;
    int ret;
 
    ast_mutex_lock(&enumlock);
 
    ast_verb(4, "blr_txt()  cc='%s', suffix='%s', c_bl='%s'\n", cc, suffix, ienum_branchlabel);
 
    if (sizeof(domain) < (strlen(cc) * 2 + strlen(ienum_branchlabel) + strlen(suffix) + 2)) {
        ast_mutex_unlock(&enumlock);
        ast_log(LOG_WARNING, "ERROR: string sizing in blr_txt.\n");
        return -1;
    }
 
    p1 = domain + snprintf(domain, sizeof(domain), "%s.", ienum_branchlabel);
    ast_mutex_unlock(&enumlock);
 
    for (p2 = (char *) cc + strlen(cc) - 1; p2 >= cc; p2--) {
        if (isdigit(*p2)) {
            *p1++ = *p2;
            *p1++ = '.';
        }
    }
    strcat(p1, suffix);
 
    ast_verb(4, "blr_txt() FQDN for TXT record: %s, cc was %s\n", domain, cc);
 
    ret = ast_search_dns(&context, domain, C_IN, T_TXT, txt_callback);
 
    if (ret > 0) {
        ret = atoi(context.txt);
 
        if ((ret >= 0) && (ret < 20)) {
            ast_verb(3, "blr_txt() BLR TXT record for %s is %d (apex: %s)\n", cc, ret, suffix);
            return ret;
        }
    }
 
    ast_verb(3, "blr_txt() BLR TXT record for %s not found (apex: %s)\n", cc, suffix);
 
    return -1;
}
 
struct ebl_context {
    unsigned char pos;
    char separator[256];        /* label to insert */
    int sep_len;            /* Length */
    char apex[256];         /* new Apex */
    int apex_len;           /* Length */
};
 
/*! \brief Callback for EBL record lookup */
static int ebl_callback(void *context, unsigned char *answer, int len, unsigned char *fullanswer)
{
    struct ebl_context *c = context;
    int i;
 
    c->pos = 0; /* default to empty */
    c->separator[0] = 0;
    c->sep_len = 0;
    c->apex[0] = 0;
    c->apex_len = 0;
 
    if (answer == NULL) {
        return 0;
    }
 
    /* draft-lendl-enum-branch-location-record-00
     *
     *      0  1  2  3  4  5  6  7
     *    +--+--+--+--+--+--+--+--+
     *    |       POSITION        |
     *    +--+--+--+--+--+--+--+--+
     *    /       SEPARATOR       /
     *    +--+--+--+--+--+--+--+--+
     *    /         APEX          /
     *    +--+--+--+--+--+--+--+--+
     *
     *  where POSITION is a single byte, SEPARATOR is a <character-string>
     *  and APEX is a <domain-name>.
     *
     */
 
    c->pos = *answer++;
    len -= 1;
 
    if ((c->pos > 15) || len < 2) { /* illegal packet */
        ast_log(LOG_WARNING, "ebl_callback: malformed EBL record.\n");
        return 0;
    }
 
    i = *answer++;
    len -= 1;
    if (i > len) {  /* illegal packet */
        ast_log(LOG_WARNING, "ebl_callback: malformed EBL record.\n");
        return 0;
    }
 
    ast_copy_string(c->separator, (char *)answer, i + 1);
    c->sep_len = i;
 
    answer += i;
    len -= i;
 
    if ((i = dn_expand((unsigned char *)fullanswer, (unsigned char *)answer + len,
                (unsigned char *)answer, c->apex, sizeof(c->apex) - 1)) < 0) {
        ast_log(LOG_WARNING, "Failed to expand hostname\n");
        return 0;
    }
    c->apex[i] = 0;
    c->apex_len = i;
 
    return 1;
}
 
/*! \brief Evaluate the I-ENUM branch as stored in an EBL record */
/*
 * Input: CC code
 *
 * Output: number of digits in the number before the i-enum branch
 *
 * Algorithm:  Build <ienum_branchlabel>.c.c.<suffix> and look for an EBL record
 *      Return pos and fill in separator and apex.
 *      Return -1 on not found.
 *
 */
static int blr_ebl(const char *cc, const char *suffix, char *separator, int sep_len, char* apex, int apex_len)
{
    struct ebl_context context;
    char domain[128] = "";
    char *p1,*p2;
    int ret;
 
    ast_mutex_lock(&enumlock);
 
    ast_verb(4, "blr_ebl()  cc='%s', suffix='%s', c_bl='%s'\n", cc, suffix, ienum_branchlabel);
 
    if (sizeof(domain) < (strlen(cc) * 2 + strlen(ienum_branchlabel) + strlen(suffix) + 2)) {
        ast_mutex_unlock(&enumlock);
        ast_log(LOG_WARNING, "ERROR: string sizing in blr_EBL.\n");
        return -1;
    }
 
    p1 = domain + snprintf(domain, sizeof(domain), "%s.", ienum_branchlabel);
    ast_mutex_unlock(&enumlock);
 
    for (p2 = (char *) cc + strlen(cc) - 1; p2 >= cc; p2--) {
        if (isdigit(*p2)) {
            *p1++ = *p2;
            *p1++ = '.';
        }
    }
    strcat(p1, suffix);
 
    ast_verb(4, "blr_ebl() FQDN for EBL record: %s, cc was %s\n", domain, cc);
 
    ret = ast_search_dns(&context, domain, C_IN, T_EBL, ebl_callback);
    if (ret > 0) {
        ret = context.pos;
 
        if ((ret >= 0) && (ret < 20)) {
            ast_verb(3, "blr_txt() BLR EBL record for %s is %d/%s/%s)\n", cc, ret, context.separator, context.apex);
            ast_copy_string(separator, context.separator, sep_len);
            ast_copy_string(apex, context.apex, apex_len);
            return ret;
        }
    }
    ast_verb(3, "blr_txt() BLR EBL record for %s not found (apex: %s)\n", cc, suffix);
    return -1;
}
 
/*! \brief Parse NAPTR record information elements */
static unsigned int parse_ie(char *data, unsigned int maxdatalen, unsigned char *src, unsigned int srclen)
{
    unsigned int len, olen;
 
    len = olen = (unsigned int) src[0];
    src++;
    srclen--;
 
    if (len > srclen) {
        ast_log(LOG_WARNING, "ENUM parsing failed: Wanted %u characters, got %u\n", len, srclen);
        return -1;
    }
 
    if (len > maxdatalen)
        len = maxdatalen;
    memcpy(data, src, len);
 
    return olen + 1;
}
 
/*! \brief Parse DNS NAPTR record used in ENUM ---*/
static int parse_naptr(unsigned char *dst, int dstsize, char *tech, int techsize, unsigned char *answer, int len, unsigned char *naptrinput)
{
    char tech_return[80];
    char *oanswer = (char *)answer;
    char flags[512] = "";
    char services[512] = "";
    char *p;
    char regexp[512] = "";
    char repl[512] = "";
    char tempdst[512] = "";
    char errbuff[512] = "";
    char delim;
    char *delim2;
    char *pattern, *subst, *d;
    int res;
    int regexp_len, rc;
    static const int max_bt = 10; /* max num of regexp backreference allowed, must remain 10 to guarantee a valid backreference index */
    int size, matchindex; /* size is the size of the backreference sub. */
    size_t d_len = sizeof(tempdst) - 1;
    regex_t preg;
    int re_flags = REG_EXTENDED | REG_NEWLINE;
    regmatch_t pmatch[max_bt];
 
    tech_return[0] = '\0';
    dst[0] = '\0';
 
    if (len < sizeof(struct naptr)) {
        ast_log(LOG_WARNING, "NAPTR record length too short\n");
        return -1;
    }
    answer += sizeof(struct naptr);
    len -= sizeof(struct naptr);
    if ((res = parse_ie(flags, sizeof(flags) - 1, answer, len)) < 0) {
        ast_log(LOG_WARNING, "Failed to get flags from NAPTR record\n");
        return -1;
    } else {
        answer += res;
        len -= res;
    }
 
    if ((res = parse_ie(services, sizeof(services) - 1, answer, len)) < 0) {
        ast_log(LOG_WARNING, "Failed to get services from NAPTR record\n");
        return -1;
    } else {
        answer += res;
        len -= res;
    }
    if ((res = parse_ie(regexp, sizeof(regexp) - 1, answer, len)) < 0) {
        ast_log(LOG_WARNING, "Failed to get regexp from NAPTR record\n");
        return -1;
    } else {
        answer += res;
        len -= res;
    }
 
    if ((res = dn_expand((unsigned char *)oanswer, (unsigned char *)answer + len, (unsigned char *)answer, repl, sizeof(repl) - 1)) < 0) {
        ast_log(LOG_WARNING, "Failed to expand hostname\n");
        return -1;
    }
 
    ast_debug(3, "NAPTR input='%s', flags='%s', services='%s', regexp='%s', repl='%s'\n",
        naptrinput, flags, services, regexp, repl);
 
 
    if (tolower(flags[0]) != 'u') {
        ast_log(LOG_WARNING, "NAPTR Flag must be 'U' or 'u'.\n");
        return -1;
    }
 
    p = strstr(services, "e2u+");
    if (p == NULL)
        p = strstr(services, "E2U+");
    if (p){
        p = p + 4;
        if (strchr(p, ':')){
            p = strchr(p, ':') + 1;
        }
        ast_copy_string(tech_return, p, sizeof(tech_return));
    } else {
 
        p = strstr(services, "+e2u");
        if (p == NULL)
            p = strstr(services, "+E2U");
        if (p) {
            *p = 0;
            p = strchr(services, ':');
            if (p)
                *p = 0;
            ast_copy_string(tech_return, services, sizeof(tech_return));
        }
    }
 
    regexp_len = strlen(regexp);
    if (regexp_len < 7) {
        ast_log(LOG_WARNING, "Regex too short to be meaningful.\n");
        return -1;
    }
 
    /* this takes the first character of the regexp (which is a delimiter)
     * and uses that character to find the index of the second delimiter */
    delim = regexp[0];
    delim2 = strchr(regexp + 1, delim);
    if ((delim2 == NULL)
        || ((regexp[regexp_len - 1] != 'i' || regexp[regexp_len - 2] != delim)
            && regexp[regexp_len - 1] != delim)) {
        ast_log(LOG_WARNING, "Regex delimiter error (on \"%s\").\n", regexp);
        return -1;
    } else if (strchr((delim2 + 1), delim) == NULL) { /* if the second delimiter is found, make sure there is a third instance.  this could be the end one instead of the middle */
        ast_log(LOG_WARNING, "Regex delimiter error (on \"%s\").\n", regexp);
        return -1;
    }
 
    /* Make the regex case-insensitive if the 'i' flag is present. This assumes you
     * aren't using 'i' as a delimiter which, although dubious, does not appear to be
     * explicitly non-compliant */
    if (regexp[regexp_len - 1] == 'i') {
        re_flags |= REG_ICASE;
    }
 
    pattern = regexp + 1;   /* pattern is the regex without the begining and ending delimiter */
    *delim2 = 0;    /* zero out the middle delimiter */
    subst   = delim2 + 1; /* dst substring is everything after the second delimiter. */
    regexp[regexp_len - 1] = 0; /* zero out the last delimiter */
 
/*
 * now do the regex wizardry.
 */
 
    if (regcomp(&preg, pattern, re_flags)) {
        ast_log(LOG_WARNING, "NAPTR Regex compilation error (regex = \"%s\").\n", regexp);
        return -1;
    }
 
    if (preg.re_nsub > ARRAY_LEN(pmatch)) {
        ast_log(LOG_WARNING, "NAPTR Regex compilation error: too many subs.\n");
        regfree(&preg);
        return -1;
    }
    /* pmatch is an array containing the substring indexes for the regex backreference sub.
     * max_bt is the maximum number of backreferences allowed to be stored in pmatch */
    if ((rc = regexec(&preg, (char *) naptrinput, max_bt, pmatch, 0))) {
        regerror(rc, &preg, errbuff, sizeof(errbuff));
        ast_log(LOG_WARNING, "NAPTR Regex match failed. Reason: %s\n", errbuff);
        regfree(&preg);
        return -1;
    }
    regfree(&preg);
 
    d = tempdst;
    d_len--;
 
    /* perform the backreference sub. Search the subst for backreferences,
     * when a backreference is found, retrieve the backreferences number.
     * use the backreference number as an index for pmatch to retrieve the
     * beginning and ending indexes of the substring to insert as the backreference.
     * if no backreference is found, continue copying the subst into tempdst */
    while (*subst && (d_len > 0)) {
        if ((subst[0] == '\\') && isdigit(subst[1])) { /* is this character the beginning of a backreference */
            matchindex = (int) (subst[1] - '0');
            if (matchindex >= ARRAY_LEN(pmatch)) {
                ast_log(LOG_WARNING, "Error during regex substitution. Invalid pmatch index.\n");
                return -1;
            }
            /* pmatch len is 10. we are guaranteed a single char 0-9 is a valid index */
            size = pmatch[matchindex].rm_eo - pmatch[matchindex].rm_so;
            if (size > d_len) {
                ast_log(LOG_WARNING, "Not enough space during NAPTR regex substitution.\n");
                return -1;
            }
            /* are the pmatch indexes valid for the input length */
            if ((strlen((char *) naptrinput) >= pmatch[matchindex].rm_eo) && (pmatch[matchindex].rm_so <= pmatch[matchindex].rm_eo)) {
                memcpy(d, (naptrinput + (int) pmatch[matchindex].rm_so), size);  /* copy input substring into backreference marker */
                d_len -= size;
                subst += 2;  /* skip over backreference characters to next valid character */
                d += size;
            } else {
                ast_log(LOG_WARNING, "Error during regex substitution. Invalid backreference index.\n");
                return -1;
            }
        } else if (isprint(*subst)) {
            *d++ = *subst++;
            d_len--;
        } else {
            ast_log(LOG_WARNING, "Error during regex substitution.\n");
            return -1;
        }
    }
    *d = 0;
    ast_copy_string((char *) dst, tempdst, dstsize);
    dst[dstsize - 1] = '\0';
 
    if (*tech != '\0'){ /* check if it is requested NAPTR */
        if (!strncasecmp(tech, "ALL", techsize)){
            return 0; /* return or count any RR */
        }
        if (!strncasecmp(tech_return, tech, sizeof(tech_return) < techsize ? sizeof(tech_return): techsize)){
            ast_copy_string(tech, tech_return, techsize);
            return 0; /* we got our RR */
        } else { /* go to the next RR in the DNS answer */
            return 1;
        }
    }
 
    /* tech was not specified, return first parsed RR */
    ast_copy_string(tech, tech_return, techsize);
 
    return 0;
}
 
/* do not return requested value, just count RRs and return thei number in dst */
#define ENUMLOOKUP_OPTIONS_COUNT       1
/* do an ISN style lookup */
#define ENUMLOOKUP_OPTIONS_ISN      2
/* do a infrastructure ENUM lookup */
#define ENUMLOOKUP_OPTIONS_IENUM    4
/* do a direct DNS lookup: no reversal */
#define ENUMLOOKUP_OPTIONS_DIRECT   8
 
/*! \brief Callback from ENUM lookup function */
static int enum_callback(void *context, unsigned char *answer, int len, unsigned char *fullanswer)
{
    struct enum_context *c = context;
    void *p = NULL;
    int res;
 
    res = parse_naptr((unsigned char *)c->dst, c->dstlen, c->tech, c->techlen, answer, len, (unsigned char *)c->naptrinput);
 
    if (res < 0) {
        ast_log(LOG_WARNING, "Failed to parse naptr\n");
        return -1;
    } else if ((res == 0) && !ast_strlen_zero(c->dst)) { /* ok, we got needed NAPTR */
        if (c->options & ENUMLOOKUP_OPTIONS_COUNT) { /* counting RRs */
            c->count++;
            snprintf(c->dst, c->dstlen, "%d", c->count);
        } else  {
            if ((p = ast_realloc(c->naptr_rrs, sizeof(*c->naptr_rrs) * (c->naptr_rrs_count + 1)))) {
                c->naptr_rrs = p;
                memcpy(&c->naptr_rrs[c->naptr_rrs_count].naptr, answer, sizeof(c->naptr_rrs->naptr));
                c->naptr_rrs[c->naptr_rrs_count].result = ast_strdup(c->dst);
                c->naptr_rrs[c->naptr_rrs_count].tech = ast_strdup(c->tech);
                c->naptr_rrs[c->naptr_rrs_count].sort_pos = c->naptr_rrs_count;
                c->naptr_rrs_count++;
            }
            c->dst[0] = 0;
        }
        return 0;
    }
 
    return 0;
}
 
/* ENUM lookup */
int ast_get_enum(struct ast_channel *chan, const char *number, char *dst, int dstlen, char *tech, int techlen, char* suffix, char* options, unsigned int record, struct enum_context **argcontext)
{
    struct enum_context *context;
    char tmp[512];
    char domain[256];
    char left[128];
    char middle[128];
    char naptrinput[128];
    char apex[128] = "";
    int ret = -1;
    /* for ISN rewrite */
    char *p1 = NULL;
    char *p2 = NULL;
    char *p3 = NULL;
    int k = 0;
    int i = 0;
    int z = 0;
    int spaceleft = 0;
    struct timeval time_start, time_end;
 
    if (ast_strlen_zero(suffix)) {
        ast_log(LOG_WARNING, "ast_get_enum need a suffix parameter now.\n");
        return -1;
    }
 
    ast_debug(2, "num='%s', tech='%s', suffix='%s', options='%s', record=%u\n", number, tech, suffix, options, record);
 
/*
  We don't need that any more, that "n" preceding the number has been replaced by a flag
  in the options paramter.
    ast_copy_string(naptrinput, number, sizeof(naptrinput));
*/
/*
 * The "number" parameter includes a leading '+' if it's a full E.164 number (and not ISN)
 * We need to preserve that as the regex inside NAPTRs expect the +.
 *
 * But for the domain generation, the '+' is a nuisance, so we get rid of it.
*/
    ast_copy_string(naptrinput, number[0] == 'n' ? number + 1 : number, sizeof(naptrinput));
    if (number[0] == '+') {
        number++;
    }
 
    if (!(context = ast_calloc(1, sizeof(*context)))) {
        return -1;
    }
 
    if ((p3 = strchr(naptrinput, '*'))) {
        *p3='\0';
    }
 
    context->naptrinput = naptrinput;   /* The number */
    context->dst = dst;         /* Return string */
    context->dstlen = dstlen;
    context->tech = tech;
    context->techlen = techlen;
    context->options = 0;
    context->position = record > 0 ? record : 1;
    context->count = 0;
    context->naptr_rrs = NULL;
    context->naptr_rrs_count = 0;
 
    /*
     * Process options:
     *
     *  c   Return count, not URI
     *  i   Use infrastructure ENUM
     *  s   Do ISN transformation
     *  d   Direct DNS query: no reversing.
     *
     */
    if (options != NULL) {
        if (strchr(options,'s')) {
            context->options |= ENUMLOOKUP_OPTIONS_ISN;
        } else if (strchr(options,'i')) {
            context->options |= ENUMLOOKUP_OPTIONS_IENUM;
        } else if (strchr(options,'d')) {
            context->options |= ENUMLOOKUP_OPTIONS_DIRECT;
        }
        if (strchr(options,'c')) {
            context->options |= ENUMLOOKUP_OPTIONS_COUNT;
        }
        if (strchr(number,'*')) {
            context->options |= ENUMLOOKUP_OPTIONS_ISN;
        }
    }
    ast_debug(2, "ENUM options(%s): pos=%d, options='%d'\n", options, context->position, context->options);
    ast_debug(1, "n='%s', tech='%s', suffix='%s', options='%d', record='%d'\n",
            number, tech, suffix, context->options, context->position);
 
    /*
     * This code does more than simple RFC3261 ENUM. All these rewriting
     * schemes have in common that they build the FQDN for the NAPTR lookup
     * by concatenating
     *    - a number which needs be flipped and "."-seperated   (left)
     *    - some fixed string                   (middle)
     *    - an Apex.                        (apex)
     *
     * The RFC3261 ENUM is: left=full number, middle="", apex=from args.
     * ISN:  number = "middle*left", apex=from args
     * I-ENUM: EBL parameters build the split, can change apex
     * Direct: left="", middle=argument, apex=from args
     *
     */
 
    /* default: the whole number will be flipped, no middle domain component */
    ast_copy_string(left, number, sizeof(left));
    middle[0] = '\0';
    /*
     * I-ENUM can change the apex, thus we copy it
     */
    ast_copy_string(apex, suffix, sizeof(apex));
    /* ISN rewrite */
    if ((context->options & ENUMLOOKUP_OPTIONS_ISN) && (p1 = strchr(number, '*'))) {
        *p1++ = '\0';
        ast_copy_string(left, number, sizeof(left));
        ast_copy_string(middle, p1, sizeof(middle) - 1);
        strcat(middle, ".");
        ast_debug(2, "ISN ENUM: left=%s, middle='%s'\n", left, middle);
    /* Direct DNS lookup rewrite */
    } else if (context->options & ENUMLOOKUP_OPTIONS_DIRECT) {
        left[0] = 0; /* nothing to flip around */
        ast_copy_string(middle, number, sizeof(middle) - 1);
        strcat(middle, ".");
        ast_debug(2, "DIRECT ENUM:  middle='%s'\n", middle);
    /* Infrastructure ENUM rewrite */
    } else if (context->options & ENUMLOOKUP_OPTIONS_IENUM) {
        int sdl = 0;
        char cc[8];
        char sep[256], n_apex[256];
        int cc_len = cclen(number);
        sdl = cc_len;
        ast_mutex_lock(&enumlock);
        ast_copy_string(sep, ienum_branchlabel, sizeof(sep)); /* default */
        ast_mutex_unlock(&enumlock);
 
        switch (ebl_alg) {
        case ENUMLOOKUP_BLR_EBL:
            ast_copy_string(cc, number, cc_len); /* cclen() never returns more than 3 */
            sdl = blr_ebl(cc, suffix, sep, sizeof(sep) - 1, n_apex, sizeof(n_apex) - 1);
 
            if (sdl >= 0) {
                ast_copy_string(apex, n_apex, sizeof(apex));
                ast_debug(2, "EBL ENUM: sep=%s, apex='%s'\n", sep, n_apex);
            } else {
                sdl = cc_len;
            }
            break;
        case ENUMLOOKUP_BLR_TXT:
            ast_copy_string(cc, number, cc_len); /* cclen() never returns more than 3 */
            sdl = blr_txt(cc, suffix);
 
            if (sdl < 0) {
                sdl = cc_len;
            }
            break;
 
        case ENUMLOOKUP_BLR_CC: /* BLR is at the country-code level */
        default:
            sdl = cc_len;
            break;
        }
 
        if (sdl > strlen(number)) { /* Number too short for this sdl? */
            ast_log(LOG_WARNING, "I-ENUM: subdomain location %d behind number %s\n", sdl, number);
            ast_free(context);
            return 0;
        }
        ast_copy_string(left, number + sdl, sizeof(left));
 
        ast_mutex_lock(&enumlock);
        ast_copy_string(middle, sep, sizeof(middle) - 1);
        strcat(middle, ".");
        ast_mutex_unlock(&enumlock);
 
        /* check the space we need for middle */
        if ((sdl * 2 + strlen(middle) + 2) > sizeof(middle)) {
            ast_log(LOG_WARNING, "ast_get_enum: not enough space for I-ENUM rewrite.\n");
            ast_free(context);
            return -1;
        }
 
        p1 = middle + strlen(middle);
        for (p2 = (char *) number + sdl - 1; p2 >= number; p2--) {
            if (isdigit(*p2)) {
                *p1++ = *p2;
                *p1++ = '.';
            }
        }
        *p1 = '\0';
 
        ast_debug(2, "I-ENUM: cclen=%d, left=%s, middle='%s', apex='%s'\n", cc_len, left, middle, apex);
    }
 
    if (strlen(left) * 2 + 2 > sizeof(domain)) {
        ast_log(LOG_WARNING, "string to long in ast_get_enum\n");
        ast_free(context);
        return -1;
    }
 
    /* flip left into domain */
    p1 = domain;
    for (p2 = left + strlen(left); p2 >= left; p2--) {
        if (isdigit(*p2)) {
            *p1++ = *p2;
            *p1++ = '.';
        }
    }
    *p1 = '\0';
 
    if (chan && ast_autoservice_start(chan) < 0) {
        ast_free(context);
        return -1;
    }
 
    spaceleft = sizeof(tmp) - 2;
    ast_copy_string(tmp, domain, spaceleft);
    spaceleft -= strlen(domain);
 
    if (*middle) {
        strncat(tmp, middle, spaceleft);
        spaceleft -= strlen(middle);
    }
 
    strncat(tmp,apex,spaceleft);
    time_start = ast_tvnow();
    ret = ast_search_dns(context, tmp, C_IN, T_NAPTR, enum_callback);
    time_end = ast_tvnow();
 
    ast_debug(2, "profiling: %s, %s, %" PRIi64 " ms\n",
            (ret == 0) ? "OK" : "FAIL", tmp, ast_tvdiff_ms(time_end, time_start));
 
    if (ret < 0) {
        ast_debug(1, "No such number found: %s (%s)\n", tmp, strerror(errno));
        context->naptr_rrs_count = -1;
        strcpy(dst, "0");
        ret = 0;
    }
 
    if (context->naptr_rrs_count >= context->position && ! (context->options & ENUMLOOKUP_OPTIONS_COUNT)) {
        /* sort array by NAPTR order/preference */
        for (k = 0; k < context->naptr_rrs_count; k++) {
            for (i = 0; i < context->naptr_rrs_count; i++) {
                /* use order first and then preference to compare */
                if ((ntohs(context->naptr_rrs[k].naptr.order) < ntohs(context->naptr_rrs[i].naptr.order)
                     && context->naptr_rrs[k].sort_pos > context->naptr_rrs[i].sort_pos)
                     || (ntohs(context->naptr_rrs[k].naptr.order) > ntohs(context->naptr_rrs[i].naptr.order)
                     && context->naptr_rrs[k].sort_pos < context->naptr_rrs[i].sort_pos)) {
                    z = context->naptr_rrs[k].sort_pos;
                    context->naptr_rrs[k].sort_pos = context->naptr_rrs[i].sort_pos;
                    context->naptr_rrs[i].sort_pos = z;
                    continue;
                }
                if (ntohs(context->naptr_rrs[k].naptr.order) == ntohs(context->naptr_rrs[i].naptr.order)) {
                    if ((ntohs(context->naptr_rrs[k].naptr.pref) < ntohs(context->naptr_rrs[i].naptr.pref)
                         && context->naptr_rrs[k].sort_pos > context->naptr_rrs[i].sort_pos)
                         || (ntohs(context->naptr_rrs[k].naptr.pref) > ntohs(context->naptr_rrs[i].naptr.pref)
                         && context->naptr_rrs[k].sort_pos < context->naptr_rrs[i].sort_pos)) {
                        z = context->naptr_rrs[k].sort_pos;
                        context->naptr_rrs[k].sort_pos = context->naptr_rrs[i].sort_pos;
                        context->naptr_rrs[i].sort_pos = z;
                    }
                }
            }
        }
        for (k = 0; k < context->naptr_rrs_count; k++) {
            if (context->naptr_rrs[k].sort_pos == context->position - 1) {
                ast_copy_string(context->dst, context->naptr_rrs[k].result, dstlen);
                ast_copy_string(context->tech, context->naptr_rrs[k].tech, techlen);
                break;
            }
        }
    } else if (!(context->options & ENUMLOOKUP_OPTIONS_COUNT)) {
        context->dst[0] = 0;
    } else if ((context->options & ENUMLOOKUP_OPTIONS_COUNT)) {
        snprintf(context->dst, context->dstlen, "%d", context->naptr_rrs_count + context->count);
    }
 
    if (chan) {
        ret |= ast_autoservice_stop(chan);
    }
 
    if (!argcontext) {
        for (k = 0; k < context->naptr_rrs_count; k++) {
            ast_free(context->naptr_rrs[k].result);
            ast_free(context->naptr_rrs[k].tech);
        }
        ast_free(context->naptr_rrs);
        ast_free(context);
    } else {
        *argcontext = context;
    }
 
    return ret;
}
 
/*! \internal
 * \brief Format a phone number as a domain in an ENUM-adjacent way.
 *
 * Creates a domain name suitable for query by:
 *
 * 1. Removing non-digits
 * 2. Adding a '.' between adjacent digits
 * 3. Reversing the string
 * 4. Appending the specified suffix (or e164.arpa if none is specified)
 */
static char *format_numeric_domain(const char *number, const char *suffix)
{
    char *buffer, *dst;
    size_t suffix_length;
    size_t number_length = strlen(number);
    const char *src = number + number_length - 1;
 
    if (!suffix) {
        suffix = "e164.arpa";
    }
 
    suffix_length = strlen(suffix);
 
    dst = buffer = ast_malloc(
        (number_length * 2) /* We need 2 bytes per input digit */
        + suffix_length     /* ... plus however long the suffix is */
        + 1                 /* ... plus room for the '.' separator */
        + 1                 /* ... and room for the \0 byte at the end */);
 
    if (buffer) {
        while (src >= number) {
            if (isdigit(*src)) {
                *dst++ = *src;
                *dst++ = '.';
            }
            src--;
        }
 
        /* The length arguments below make sure that the \0 byte is copied into
           the final string */
        if (*suffix == '.') {
            memcpy(dst, &suffix[1], suffix_length);
        } else {
            memcpy(dst, suffix, suffix_length + 1);
        }
    }
 
    return buffer;
}
 
int ast_get_txt(struct ast_channel *chan, const char *number, char *txt, int txtlen, char *suffix)
{
    struct txt_context context;
    char *domain;
    int ret;
    int autoservice = 0;
 
    ast_debug(4, "ast_get_txt: Number = '%s', suffix = '%s'\n", number, suffix);
 
    domain = format_numeric_domain(number, suffix);
    if (!domain) {
        return -1;
    }
 
    if (chan) {
        /* DNS might take a while, so service the channel while we're blocked */
        autoservice = !ast_autoservice_start(chan);
    }
 
    ret = ast_search_dns(&context, domain, C_IN, T_TXT, txt_callback);
    if (ret > 0) {
        ast_copy_string(txt, context.txt, txtlen);
    } else {
        ast_debug(2, "No such number found in ENUM: %s (%s)\n", domain, strerror(errno));
    }
 
    if (autoservice) {
        ast_autoservice_stop(chan);
    }
 
    ast_free(domain);
    return 0;
}
 
/*! \brief Initialize the ENUM support subsystem */
static int private_enum_init(int reload)
{
    struct ast_config *cfg;
    const char *string;
    struct ast_flags config_flags = { reload ? CONFIG_FLAG_FILEUNCHANGED : 0 };
 
    if ((cfg = ast_config_load2("enum.conf", "enum", config_flags)) == CONFIG_STATUS_FILEUNCHANGED)
        return 0;
    if (cfg == CONFIG_STATUS_FILEMISSING || cfg == CONFIG_STATUS_FILEUNCHANGED || cfg == CONFIG_STATUS_FILEINVALID) {
        return 0;
    }
 
    /* Destroy existing list */
    ast_mutex_lock(&enumlock);
    if (cfg) {
        if ((string = ast_variable_retrieve(cfg, "ienum", "branchlabel"))) {
            ast_copy_string(ienum_branchlabel, string, sizeof(ienum_branchlabel));
        }
 
        if ((string = ast_variable_retrieve(cfg, "ienum", "ebl_alg"))) {
            ebl_alg = ENUMLOOKUP_BLR_CC; /* default */
 
            if (!strcasecmp(string, "txt"))
                ebl_alg = ENUMLOOKUP_BLR_TXT;
            else if (!strcasecmp(string, "ebl"))
                ebl_alg = ENUMLOOKUP_BLR_EBL;
            else if (!strcasecmp(string, "cc"))
                ebl_alg = ENUMLOOKUP_BLR_CC;
            else
                ast_log(LOG_WARNING, "No valid parameter for ienum/ebl_alg.\n");
        }
        ast_config_destroy(cfg);
    }
    ast_mutex_unlock(&enumlock);
    return 0;
}
 
static int load_module(void)
{
    return private_enum_init(0) ? AST_MODULE_LOAD_FAILURE : AST_MODULE_LOAD_SUCCESS;
}
 
static int unload_module(void)
{
    return 0;
}
 
static int reload_module(void)
{
    return private_enum_init(1);
}
 
AST_MODULE_INFO(ASTERISK_GPL_KEY, AST_MODFLAG_GLOBAL_SYMBOLS | AST_MODFLAG_LOAD_ORDER, "ENUM Support",
    .support_level = AST_MODULE_SUPPORT_CORE,
    .load = load_module,
    .unload = unload_module,
    .reload = reload_module,
    .load_pri = AST_MODPRI_CORE,
    .requires = "extconfig",
);